In gang machines which perform substantially the same machining operation on each of a plurality of workpieces at the same time, it has been the usual practice to locate and manually clamp the plurality of workpieces on a pallet. The pallet with the workpieces on it is then transferred into the gang machine while substantially the same machining operation such as drilling a hole is performed on all the workpieces on the pallet.
Pallets with a group of workpieces clamped on them are usually advanced through the gang machine by a transfer mechanism. When machining of each group of workpieces has been completed, the pallet is transferred out of the machine as the workpieces are unclamped and removed from the pallet, usually by hand. The pallet is then cleaned, reloaded with workpieces to be machined, and advanced by the transfer through the gang machine again.
Frequently the workpieces are loaded on the pallet and unloaded from the pallet mechanically by the use of robots or specially designed loaders. To locate and clamp the workpieces on the pallet with sufficient precision it is usually necessary to manually locate and hold the workpieces while they are clamped to the pallet.
Frequently, each pallet of workpieces is transferred through several gang machines, in each of which a machining operation is performed on all of the workpieces to produce finished workpieces. For example, to produce a threaded hole in each workpiece, the hole may be partially drilled in each of three gang drilling machines, the drilled hole reamed in a gang reaming machine and threads cut in the drilled and reamed hole by a gang tapping machine.